.out{
  width: 400px;
  height: 400px;
  margin: 100px auto;
  border:solid 1px #345;
  position:relative;
}

.inner{
  width: 100px;
  height: 100px;
  background:#aef;
  border-radius: 50%;
  position:absolute;
  left: 0;
  top:0;
}